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I believe an implementation of the answer by Peter Taylor above would be:

```cs
public override EntityEntry<TEntity> Add<TEntity>([NotNullAttribute] TEntity entity)
    where TEntity : class
{
    return Add(entity, base.Add);
}

public TEntityEntry_TEntity Add<TEntity, TEntityEntry_TEntity>([NotNullAttribute] TEntity entity,
    [NotNullAttribute] Func<TEntity, TEntityEntry_TEntity> wrap)
    where TEntity : class
    where TEntityEntry_TEntity : EntityEntry
{
    return wrap(entity);
}
```